Derivatives and Hedge Accounting Activities (Schedule of Offsetting Assets) (Detail) - USD ($) $ in Millions	Mar. 31, 2018		Dec. 31, 2017
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	$ 240		$ 303
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	240		303
Total derivatives, not subject to a master netting or similar arrangement	4		4
Gross Amounts of Recognized Assets, Total	244		307
Derivative Asset	244		307
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	34		99
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	206		204
Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	124		155
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	124		155
Total derivatives, not subject to a master netting or similar arrangement	5		11
Gross Amounts of Recognized Assets, Total	129		166
Derivative Asset	129	[1]	166
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	5		4
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	119		151
Dominion Energy Gas Holdings, LLC
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	44		32
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	44		32
Derivative Asset	44		32
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	1		2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	43		30
Commodity | Over-the-counter
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	132		174
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	132		174
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	5		9
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	127		165
Commodity | Over-the-counter | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	118		155
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	118		155
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	2		4
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	116		151
Commodity | Exchange
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	20		80
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	20		80
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	19		80
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	1		0
Interest rate | Over-the-counter
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	44		17
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	44		17
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	9		8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	35		9
Interest rate | Over-the-counter | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	6		0
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	6		0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	3		0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	3		0
Foreign currency | Over-the-counter
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	44		32
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	44		32
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	1		2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	43		30
Foreign currency | Over-the-counter | Dominion Energy Gas Holdings, LLC
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	44		32
Gross Amounts Offset in the Consolidated Balance Sheet	0		0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	44		32
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	1		2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0		0
Net Amounts	$ 43		$ 30

[1] Noncurrent derivative assets are presented in other deferred charges and other assets in Virginia Power's Consolidated Balance Sheets.